The present invention relates to adjustment assemblies for actuators, and more particularly to adjustment assemblies for use with ram air turbine (RAT) actuators.
Modern aircraft often include a secondary or emergency power system that can provide power in the event that power is unavailable from a primary power system. RATs are commonly used for secondary or emergency power systems to provide electrical and/or hydraulic power. A typical RAT is deployable in flight by opening suitable doors or hatches in the aircraft's fuselage. The RAT presents a rotatable turbine to oncoming airflow, which rotates the turbine. Rotational energy (torque) from the turbine is then transmitted to a suitable power conversion device (e.g., generator, pump, etc.) that converts that rotational energy to a desired form for use by the aircraft.
RATs commonly include an actuator assembly with a spring bias mechanism and a hydraulic cylinder. The spring bias member can provide force to move the RAT from a stowed position to a deployed position, when a stow-lock mechanism is released. The hydraulic cylinder can be used to retract the RAT from the deployed position to the stowed position.
The RAT stowage compartment (or bay) and its access door(s) are sized to stow the RAT and its actuator assembly with only relatively small clearances. Operators must generally adjust RAT actuator assemblies in order to ensure that the RAT does not contact other components. Typical adjustment of prior art RAT actuator assemblies was accomplished by rotating a threaded link member in half turn increments. The threaded link had an attachment that connects to a clevis member, and therefore to permit attachment to the clevis could only be adjusted in half turn increments. Half turn increments provided only coarse actuator adjustment. A deploy cylinder of the hydraulic cylinder is then turned to make a fine adjustment. Both of these adjustments required disconnection of certain parts to allow for threaded rotation.
Furthermore, RAT actuator assemblies are traditionally adjusted for overall length only in the deployed position, where the spring load is minimized so there is no adverse wear on the locking pawls. Adjustment in the stowed position is not recommended because of pawl wear, because of the extra friction load imposed by a loaded actuation spring. Also, operator safety has dictated RAT actuator adjustment only in the deployed position, because disconnecting actuator assemblies for threaded rotation under high actuator spring loading may present dangers.
The RAT-to-door clearance change may be different from one adjustment to the next, due to a non-linear door spring rate. The need to adjust the RAT only in the deployed position, coupled with spacing sensitivities in the stowed position generally leads to a tedious measure/deploy/adjust/stow cycle, which may need to be repeated numerous times before desired RAT-to-door spacing is achieved. Thus, an alternative RAT adjustment mechanism is desired.